A volumetric 3D display displays 3D images in a real 3D space. Each xe2x80x9cvoxelxe2x80x9d in a volumetric image locates actually and physically at the spatial position where it is supposed to be, and light rays travel directly from that position toward omni-directions to form a real image in the eyes of viewers. As a result, a volumetric display possesses all major elements in both physiological and psychological depth cues and allows 360xc2x0 walk-around viewing by multiple viewers without the need of special glasses.
For convenience of communication in this specification, the term xe2x80x9cvolumetric 3D imagexe2x80x9d or xe2x80x9cvolumetric imagexe2x80x9d is used to describe a 3D image that actually occupies an actual space (that is, a physical and real space) and has each of its voxels (or volumetric elements forming the image) located physically at a spatial location relative to the physical locations of other voxels. The term xe2x80x9cvolumetric 3D displayxe2x80x9d or xe2x80x9cvolumetric displayxe2x80x9d is used to represent a display system that is capable of displaying volumetric 3D images. In contrast, a 3D image displayed in perspective views on a conventional CRT monitor, or in a stereoscopic display, do not actually occupy a real space. It is displayed in a virtual space.
There have been two major types of volumetric display using scanning lasers as the image source. The first type projects the scanning laser spots directly on a moving display screen to form images [Garcia, Garcia and Williams, Batchko, Lasher et al., Belfatto]. The second type is based on the principle of two-stage excitation [Korevaar, Downing et al.], which uses the intersection of two laser beams to excite a photoluminescent media to create images. In another approach based on two-stage excitation of a photoluminescent media, two matrices of collimated beams are used to give many intersections in a volume [Thompson]. For displaying color images, the major disadvantage of direct projection of scanning lasers is the limited number of voxels. State of the art laser projection volume display reports 20,000-40,000 voxels per volume [Lasher et al.], which is good for displaying wire-frame images but not enough to render complex color images. In the case of two-stage excitation using solid materials [Downing et al.], the disadvantage is the need of three different materials for the three primary colors. In the case of two-stage excitation using gaseous materials, the main issue may be safety as typical gases used are toxic.
Another approach uses electron beams and phosphor to create images. There are also two types of systems: one uses a moving screen coated with phosphor to receive electron beams emitted from stationary sources[Blundell], and one based on two-stage excitation of a phosphorescent gas[Rowe]. In the rotating screen approach, it would require precise registration of electron beams to phosphors of different colors on a screen which is constantly rotating. As to the two-stage excitation approach by electron beams, it would be difficult to display color images.
Another approach of volumetric display uses a rotating LED (light emitting diode) panel[Berlin]. Optic fibers have also been used to replace LEDs [MacFarlane]. The main issue of this approach is the complexity of assembling the matrix of light sources.
Still another category of volumetric display uses xe2x80x9cwhole frame displayxe2x80x9d instead of xe2x80x9cpoint scanningxe2x80x9d of lasers or electron beams. One approach uses a stack of electrically switchable liquid crystal display layers[Hattori, Sadovinik]. Another approach uses a piezo-based fast focusing lens to project image frames to a stack of PDLC screens [Paek]. Both approaches have limited resolution because the number of LCD panels or screens in the stack is physically limited. Still another approach projects images composed of collimated light beams directly to a moving screen [Thompson]. A different approach using an optical interfacing mechanism, which smoothly delivers whole frame images created on a stationary projection device onto a moving screen (rotating or reciprocating), allows creation of volumetric 3D images using conventional 2D projection optics, thus removing the requirement of collimated image beams [Tsao et al., Tsao].
To display color 3D volumetric images, approaches based on xe2x80x9cwhole frame displayxe2x80x9d, especially the one using an optical interfacing mechanism, have the advantages of high voxel number and are capable of applying many techniques used for 2D displays. Based on this approach, this invention is therefore to provide new and improved methods and systems for displaying color volumetric 3D images. This invention is also to improve the interaction between the users and the volumetric display system.
This invention relates generally to new and improved methods and apparatus for displaying volumetric 3D images with colors or gray scales. The basic concept includes four steps:
1. Process a set of raw 3D data into a viewable data: The viewable data contain a geometry description in the form of a collection of scattered points, curves and surfaces, and a corresponding color description.
2. Process the viewable data into a set of displayable data: One of four color combination methods is the used to process the viewable data into three data subsets, each of a collection of points and of a different color frequency, which can later be combined in a space to form volumetric images with colors. The four color combination methods are: (1) Exact combination: all primary colors in one voxel appears in the same location in the same volume sweep. (2) Spatial combination: primary colors for one voxel appear in slightly different locations but in the same volume sweep. (3) Temporal combination: primary colors for one voxel appear in the same location but in different volume sweeps. (4) Spatio-temporal combination: a combination of (1) and (2).
3. Generate and display a set of separate image patterns on a color display system: A set of separate image patterns, each pattern of a different color frequency, is generated on a color display system according to the content of the displayable data.
4. Recombine and display the set of separate image patterns on a volumetric display system: In the final step, the sets of separate image patterns are recombined and displayed on a volumetric display device to form color volumetric 3D images.
This invention also improves the interaction between the user and the images in the volumetric display by using a concave mirror to project the images in a volumetric display the user""s space, and by using a method of virtual manipulating device to extend user""s motion into the volumetric display space.